Field of the Invention
The present invention relates to an image forming apparatus having a mechanism for shifting a sheet with an image formed on one side in a direction perpendicular to the sheet conveyance direction when forming an image on the opposite surface of the sheet.
Description of the Related Art
Japanese Patent Application Laid-Open No. 2007-62960 discusses an image forming apparatus capable of double-sided printing, having a mechanism for shifting, in the direction perpendicular to the sheet conveyance direction, a sheet with an image printed on one side by switching back the sheet. As illustrated in FIG. 6, a sheet S picked up by a feed roller 901 is conveyed by a registration roller pair 902. A transfer roller 903 transfers a toner image onto one side of the sheet S, and then a fixing roller 904 fixes the toner image onto the sheet S.
In a case of double-sided image forming, after the trailing edge of the sheet S conveyed by a discharge reversing roller 905 passes through a point C, the discharge reversing roller 905 reversely rotates (reverses the rotational direction). Subsequently, the sheet S is shifted toward one side in the direction perpendicular to the sheet conveyance direction (i.e., in the width direction of the sheet S) by an oblique conveyance roller 906, and is abutted on a reference guide 910.
Thus, in a state where the positional accuracy of the sheet S in the width direction is guaranteed, the sheet S is conveyed by a re-feed roller 907, to the conveyance path for the first surface, and then is conveyed to the registration roller pair 902. Subsequently, after an image is formed on the back surface of the sheet S by the transfer roller 903 and the fixing roller 904, the sheet S is discharged onto a discharge tray 909 by the discharge reversing roller 905.
However, with the decrease in size of the image forming apparatus, the conveyance distance from the discharge reversing roller 905 to the re-feed roller 907 tends to decrease. Further, with the decrease in size of the image forming apparatus, the degree of the bending of the curved conveyance path tends to increase, and therefore, the frictional resistance between the sheet S and a conveyance guide increases. There has been a case where, as a result thereof, the sheet S cannot be shifted by a required amount by the oblique conveyance roller 906 to be conveyed along with the reference guide 910.